Pulse responsive circuit



Aug. 29, 1950 D. H. RANSOM PULSE RESPONSIVE CIRCUIT Filed Nov. 14, 1945 '7 Sheets-Sheet 1 COMMON EQUIPMENT I O OTHER LINKS SECOND LINK CIRCUIT LINE 8 REG RCUIT CIRCUIT FIRST LINK CIRCUIT JnEDw KMZSOA 20mm I N V EN TOR. 0/] W0 fl. FAA/50M A TTOR/VEI/ o 7 J. F 5 .2v

Aug. 29, 1950 D. H. RANSOM PliLsE RESPONSIVE CIRCUIT 7 Sheets-Sheet 2 Filed Nov. 14,- 1945 rozuaumu Ill v GE

.INVENTOR. any/0 H. /?4/V50M D. H. RANSOM 2,520,170

PULSE RESPONSIVE CIRCUIT 7 Sheets-Sheet 3 INVENTOR.

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MOE n OE Aug. 29, 1950 Filed Nov. 14, 1945 '0/2 Wu H. RIM/50M Aug. 29, 1950 0'. H. RANSOM PULSE RESPONSIVE cmcum '7 Sheets-Sheet 6 vvvvv Filed Nov. 14, 1945 3 m su Y m E D I I l l I l I |||J 6 3 m 2 M m. m m. m; I". z m 4 l 5 w m in II :IE 6 3 Llllll. 7 3 Fl-Ii FIFTH ['58- ZERO GATIEI-IJ lae 26v/ FIG. 8

ATTORNEY 1950 D. H. RANSOM PULSE RESPONSIVE CIRCUIT '7 Sheets-Sheet 7 Filed Nov. 14, 1945 FIG. 10

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- Ill/IIIIlI/Ill 1/11/11 [I INVENTOR. DAV/D IPA/$450M ATTORNEY Patented Aug. 29, 1950 um'reo s T-Ares PATENT oF-Hc-E PUL'SERESPONSIVE i CIRCUIT David H. Kansem,..Montclair, N. ..l., assignor to Federal Telephone and-Radio Corporation, New

York, N. Y., a corporation ofiDelaware ApplicationNove-mber 14, 1945; Serial "No;*628,-611

8 Claims. (Cl. 179-918) This invention relates to-pulseresponsivecircults and more particularly toemeansiforcefieotively controlling a pulseresponsive circuitior the reception of -a plurality #of signal .pulsesiof a given character.

In telephone exchange-circuits, for example, series of pulses is used to convey switching-sigrials to a central exchange, andrautomaticallyvto make the desired line selection ona-called line in cases. In. a copending-application of E. M. Deloraine, entitled Communication .Systern, Serial No. 628,613, filed-November.14,:1945, is described a telephone-exchange systemwherein signalling and comrnunicationwenergy ion-a line is divided into discrete pulses spacedapart in time and modulated. in xamplitudein accordance with the energy. The pulsesserve-toestablish and'maintain connections for vcommunication as well as is carry the communication energy. After the .callinglinelhas .been found and connection es tablishedlto: a linklcircuit, .the selector. control signals ..(selector.ldialing pulses) serve to selecttheicalled line for itheipurpose of establishing the .through communication .between the. calling and. called. line.

In accordance with my invention, I,pr.ovide:.a pulse responsive circuit which may .be iused: for the dialing pulses. This circuit provides apulse selecting circuit which selects thedialingpulses to the exclusion of communication signals. These selected dialingpulses areipassed GILtOra dial-pulse register circuit andserve to :control .the line selector for'selection of thecalledline. .In order that all the dialingpulses may be transmitted to the circuit, Iprovidemeanstomaintaima gate circuit for passing-the dial pulses to the register-openfor the period-of -.theldialing. .ilhis means prefer-ably comprises-control circuits of predetermined time .ccnstants serving .to supply the gate opening potential to .the selectordgate circuit.

The maintaining'of the pul-seselecting circuit blocked except during an \interval while the .dial pulse signals are being received prevents operation of the pulseregister-circuit.duetotransients at the beginning and end of thepulse cycle. The transients, if-passed-by this circuit, Woulddndicate a time I delay corresponding -to a different line from that to which connection is desired thus resulting inwrong-connections.

It is an-object of my inventionto proviclea pulse responsive circuit supplied with control means for maintaining thecircuit responsive for a'predetermined interval.

It is a'further objectof my invention to .pro-

videin a pulse selector circuit meansfor maintaining theoutput of .the pulse selector blocked except during-the. interval that pulse signalsr are being. received to-prevent passing of--pulses "corresponding-.110 transients through thecirouit.

It isafurther objectof. my invention-topmvide a circuit responsive .to pulses of --a predetermined character, and control means for the circuitvto. maintainit-.-open ion-a; predetermined interval. t

..It isea stilliurther .object ofsmy invention: to

provide a dial pulse responsive circuit "which serves .to select dial pulses applied 1 thereto and to pass all.these dial-pulses to asel-ector control circuit, means being provided responsive-to said selected. pulses fora maintainingsaid circuit open ,for theentire dialing interval. a I

In accordance with a feature of my invention, the .circuitiis preferably .used with asystem in whichthesignal .onspeech. currents in-thevarious lines or other channels areireplaced at theeexchange by aseriesof narrow. pulsesofampl-itude .correspon'ding .to-ihe amplitude -of the original jcurrent at .the corresponding time. ,are produced at :suflicient rapidity lso that they The pulses define substantially the signal envelope. (.In'this manner -.by callotting different time positions to each line, .thelsignal orvoice currents within-the exchange may -be .distributed over a :common channel-eachsignalbeing repeated .by a-serles .of pulses displaced .in .time 'in accordance with the distributor .timeposition. This distribution maybe readily accomplished by meansof acathodeeray .tube serving as a distributor which :will

that all these signal or dialingtpulses. areproperly applied so that'the desired.connectionismade, aipulse responsivecircuit which is maintained open .for ca period equal to the entire .pulsing interval is.provided. "This circuit serves under control of -the =dial pulses to .provide -controlpotentials to maintain the gate .circuit -.open --until dialing is -completed. 'I he time displacement means maylbeanactuahdelay lineotsomeform or an equivalent circuit which, while not producing an actual delay of the signals, will effectively serve to store the energy and release it after a predetermined interval equal to the desired delay. In this manner, the interconnection of any one line with any other line of the system may be accomplished. Upon making this interconnection, the communication signals may pass through the same delay means between the interconnected lines. Furthermore, since the scanning cycle covers each of the lines connected to the distributor, as many simultaneous connections may be made as there are time displacement trunking channels within the exchange.

Preferably, means are provided responsive to the interconnection of the lines to tie up these lines so that they cannot be selected by another subscriber attempting to get the connection. If desired, any conventional type of busy signal may be applied to the subscribers line when this condition exists so that he will know that he must wait an interval for the line to become free so that he can make the desired connection.

While I have broadly outlined certain objects and features of my invention, a better understanding of my invention and the objects and features thereof may be had from the particular description of an embodiment thereof made with reference 'to the accompanying drawings, in which:

Fig. 1 is a block diagram illustrating the general circuit set up;

Figs. 2 and 3 are sectional circuit diagrams and views respectively, of a distributor tube used in my system;

Figs. 4 to 8 inclusive, constitute a circuit diagram of a link exchange in accordance with my invention;

Fig. 4 illustrating the common equipment;

Fig. 5 showing the pulse forming equipment;

Fig. 6 the line finder equipment;

Fig. 7 the dial register equipment; and

Fig. 8 the line selecting equipment;

Fig. 9 is a diagram illustrating how Figs. 4 to 8 inclusive, should be arranged to illustrate the complete circuit;

Fig. 10 is a set of curves used in explaining the operation of certain parts of the system; and

Fig. 11 is a diagram in section of a delay line suitable for use in the equipment shown in Fig. 8.

In an example of a system incorporating the features of my invention as outlined above, the system may be divided into three parts as shown in Fig. 1: first, all the subscribers lines, twenty for example. assigned numerals l to 20, each of these lines having a subscriber sub-set equipment such as 2i; second, the equipment common to all line circuits, hereafter referred to as common equipment 22; and third, a group of link circuits one of which is needed for each simultaneous call. Each of the link circuits may be further sub-divided into line finder circuit 23, dial pulse forming circuit 24, dial register circuit 25 and line selecting circuit 26. These several major components are interconnected by wires 2148 inclusive, as shown in Fig. 1. For the sake of simplicity in the description, only one-way conversation is provided for.

As shown, all lines I to 20 terminate in common equipment 22. This equipment 22 performs a scanning function, preferably by means of a suitable tube having an electronic beam which sweeps each of the lines in turn.

When one of these lines has a potential indicative of a calling condition, the common equipment 22 applies signals over wires 21 and 28 to all the link circuits in parallel and specifically to the line finder circuit 23 of the first link (chosen for discussion). This line finder 23 operates to find the calling line and transfer the signals over wire 33 to the dial pulse forming circuit 24.

When dialing ensues, this circuit 24 produces dial pulses which are counted and stored in dial register circuit 25. The dial pulse register 25 then serves to control the line selector circuit 2;: which may comprise a delay line or other time displacement apparatus.

The incoming speech signals are then transferred from common equipment 22 over wire 28. line finder circuit 23, wire 33, line selector circuit 26 and thence over wire 36 back to the common equipment 22 from whence they are applied to the selected outgoing line. The part of Fig. 1 comprising line finder 23, dial pulse forming circuit 24, dial register 25 and line selector circuit 25 may be considered together as a link circuit. For certain embodiments of the system, a synchronizing frequency may be fed from common equipment 22 over lead 29 to line selector circuit 26 and line finder circuit 23 respectively. The five leads 21, 28, 29. 36 and 31 to and from com mon equipment 22 may also be multiplied to other link circuits of the system as shown.

The distributor function of common equipment 22 may be performed by a rotating distributor in the form of a cathode ray tube as illustrated in detail in Figs. 2 and 3. The distributor tube is indicated generally at 39 and may comprise a cathode 40. the usual grid 4!, focus and anode electrode 42, horizontal deflector plates 43 and vertical deflector plates 44. Two-phase distributor currents from a suitable sweep control may be applied over leads 45. 46, 4'! and 48 to the horizontal and vertical deflector plates respectively, so as to produce a cyclic rotation of the electron beam. At the target end of tube 39 are provided twenty coupling targets 49 to 68, respectively, which are coupled with the individual lines I to 20 inclusive. These targets may comprise secondary electron emissive element associated with a common anode 69 to provide dynodes all having a common output. A mask or screen 10 may be provided, if desired. havin apertures therein so that the electron beam will impinge on each dynode only when the beam is ali ned therewith thus preventing possible secondary emission from others. The output of the distributor tube 39 is connected from anode 69 over lead H, then signal isolat ng circuits here after described to leads 2'! and 28 which go to the line finder circuit as shown in Fig. 1. The out ut from the line selecting circuit 26 may be applied as indicated over line 36 to the grid 4| servin to modulate the beam in accordance with the selected signal energy. Thus. referring to Fig. l. the output from lead H may be applied after suitable delay (produced in line selecting equipment 26 as hereafter described) over lead 36 to grid 4! to provide the desired communication channel between the chosen pair of lines.

The common equipment 22 is illustrated in Fig. 4. For illustrative purposes a base frequency of 10,000 cycles per second has been selected as the scanning rate of the rotating distributor. This frequency is sufficiently high to reproduce voice frequencies with adequate fidelity for transmission of speech. For the twenty-line system the base frequency is derived from a 200 kilocycle stable oscillator 12 preferably crystal controlled. This higher frequency is preferably utilized since a se 170 it isgenerally easier. to build "amorestableosc-i-H latorat the higher frequencies than at the lower 1013001cycleflfrequency. whichis tOLbeused'L thermore in certain of the. modification illustrated, the 20D"ki1o.cycle Wave'may b'e-utilizedfor* other control purposes. Thesinusoidal frequencygeneratedv in master oscillator 12. is, reduced to the base frequency, of "ten kilocycles in frequency" divider. 13;

They output of frequency divider 73*isapplied over. 90 phase shift-er, to the verticaland' hori zontalisetsof deflecting platesflt" and Mtofdiss tributor. tube. as" herein diagrammatically: illus= trated... This will'serve.v to rotate the beamat 8?. frequency of 10,000 revolutions per secondso'thati Atil is illus rateda typical subscriber subeset" (shown connectedto line. for use in the systemaccording tomy invention. Such a sub-set" will. be. connected :to each. of the incoming. lines.

1.. to. 2.0linclusive. The voice, transmitter 75" is. connectedjin .serieswith dial filiand 'the. normally. open switch hook .l'l'. Thereceiven 18'. is bridged permanently cross the line, since, for simplicity of! illustration, no, separate, ringing, equipment" has..been..illustrated; Accordingly, the signalfor summoning. as. called. subscriber may be applied. specialtonewhich willbe reproduced in receiver. 13 to. call thelistener to. phone;

As inlthe. usualv equipment; switclihoolnl'l is. normally open. However, upon initiatinga call; the switch. eecomes closed, completing. a circuit inthecalling.lineloopover lowvpass filter "IQ. andthe. associatedllnes. at .thesuldeset, applying? anegative potentialfroribattery. filiito the associated. dynode, 53.. Normally, the dynode. electrodes 4 Elton 3 .areat .thesame; potentiallas .anode; 69 so .no current fiowsi. This negative potential. will produce a difference. in, potential and 1 cause. secondary. emissioncurrentto flowfromthe .d$ node, upon. impingement of. the beam. of tube. 39: thereon, producinga. negative. output. pulse in. output.1ine.'ll. The pulses. are preferably signalmodulatedto a depthofcnly 25.to..5.t.'per.-- centsothat there willalways sufiicientlamplitudeto furnishenergy toes-tablishand maintain. connections. regardless.- of modulating. signals. The negative'pulses. resulting from operation. of. the selected. dynodeare fed to. the. grid of inverter. tube, 8].. They anode. circuit. of tube. 8.! is. coupled to..-the. grid of clipper tube. 82..which. serves to. clip these pulses ata... predetermined level to pass-lcnly the modulated portions ofthe incoming.pulses.v Thus, theoutput of thistube, representing. the speech signals, may. be substane tially. 160: per. cent modulated. These; clipped. pulses arethen appliedltoacathode follower tuba 83..and fr,om there to all ofthelink circuitsoven the cathode :followeroutputlead. 35. A- second output. is .takenacrossc the cathode resistancecf inverter, tub-e35 these. pulses being applied .to.- a clipper tubetlt which. servesto clip thepulses toa constantievel eliminatin modulation effects therefrom. The. anode. circuit .of tube lid-151C011.- pledtmthe. grid of, a. cathode follower v tube. 85 which serves to apply pulses fitthroughconunon feediresisto 85!, over: wire. 25 to thegridpfiline finder. gatetubeH-S-t. (showniuFig. 5) of. line finderldlshownin Figs. 6.:and 1) in the first linkcircuit. (now underl. consideration)- and, in .par.- allel to the grids of the corresponding line finder gate tubes in all other links. The pulse86- after passing-through" resistor 8T-may be called 89; sothatr' thepulse actually arriving at the grid of tube 88 and of the other similar tubesis pulse 89: Under"tlieconditions now assumed, when none of the" grids" of the line' fi'n'der' gate tubes is drawing" grid current; pulse 89 is nearly as strong, as pulse but under other conditions it' may" be much" weaker than 86 as hereafter explained; In theabsence-of any signals'on the cathode-of"this'line finder gate tubedli, the above traced pulse 89 on itsgrid is insufficient to cause the flow of'pl'ate current, because the biasapplied to tli'e grid is sufficiently far below cutoff.

In the line-finder 23' (Figs; 1 and 6) is provided anoscillator-lillnormally operating at a frequency slightly'lower than theoutput frequency from frequency, dividerli" in- Fig; 4. This oscillator may, for-example: operate at one-fiftieth of one per cent" below the frequency of the frequency divider." The output energy from oscillator 90 isapplied to a clipperamplifier 9 I which serves to: producerectangular selecting pulses 90a. These'pulsesare. differentiated in a differentiating'networkponsisting"of condenser 92 and resistors-3, topro'ducethepulseformation 94 which is' applied to the'controlgrid of clipper tube 95. The output pulses 96' .from' tube (corresponding to'theleading'edge' of'pulse 90a. and-the positive'part" offormationi94') areappliedto cathode follower. tube 9.1; The resulting pulses 98 are applied t'otthe cathode of 'tube' 88 normally tending to. make the" cathode ofthis tube more negative soithat' the tube will be more nearly conductive. However, except when the pulses 98 applied to. thexcathode of. tube 88"coincide with thepreviously tracedincomingpulses 89, applied via wirev 2,1"to, the gridthereof; tube. 88 "is ineffective. Sufficient' biasis applied;to the grid of. tube. 88 from battery 99"so that it..requires the. combined amplitudes. ofthetwo pulses 89 and 98 to operate thistube. A's oscillator 901continues to drift relative. to. the output of. frequency divider l3, the pulses; 9K Willi commence to coincide with the pulses 891 incomingfrom the calling.line,,overcoming the biasintube BS' andiprQducing output pulses. I01]- in line. 32; These output pulses his then. areappliedoven condenser. lfll to a peaked amplifier andphase corrector. circuit H32 which servesutoilock.oscillator. Bll'into stepwith the incomingpulses 89 so. that itsoutput is in synchronism..witli= the. frequency. from. divider. 13, and pulses .98; willlthen :continue. to. coincide regularly Withtheincoming pulses :89 fromthe predeterminedcalling lineu As. soon as the. oscillator is locked'LintQstp, the. pulsesfrom 1ine32 also are applied lover. rectifier. 33L andan integrating network. I04 to a .controLgrid 10f. delayed gain control tube H15." Operation of tube )5 increases the. positivevoltage on..the.screen of clipper tube 85..increasing .the amplitude. of the outputpulses 96. and..hence.98.. Thevalheofresistor 8'l andv the. grid current; characteristics of. tube 88. are

such that'.the..totallpositive swing .of. its grid withrespectto. its. cathode .cannot exceeda predeterminedsmallilamplitude-regardless of the magnitudesnf. pulses. 98' and. 86 which are. applied re spectively, to.the.. cathode andQviaresistor 87 to the.gridlof-. tube.88I-. However, .the squarepulses 98.;from-tube. 91 will increasein amplitude with thenchangain bias of tube. 95;. Thus, since the sum.of..pul'ses:.89.and 98is roughlyconstant, while the value of the component 98 is rising, it is clear thatitheemagnitudewf. pulses-89 must be correspondingly decreasing. This decrease in amplitude of pulse 89 is efiective to prevent other line finder gate tubes (similar to 88 but in other links) from responding as more fully explained hereafter in conjunction with Fig. 10.

This decrease in pulse 89 does not, however, reduce the response of tube 88 in the first link (now under consideration) since the total input between grid and cathode is not decreased. Thus, pulses I are roughly constant in amplitude. These pulses I00 from the line finger gate tube I38 are applied also over line 32 and coupling circuit I06 to gate control tube I01 which serves to control the suppressor bias on the input gate tube I08. Tube I08 is normally conditioned by suppressor grid bias so that the pulses applied thereto from the output of cathode follower 83 over line 28 will not be passed by the tube. However, upon operation of tube I01, by selection of a predetermined incoming line as described above, the suppressor grid of tube I08 has applied to it such a potential that the tube becomes conductive during the instants corresponding to the time-channel of such predetermined line. Accordingly then, combined dial-and-speech pulses I09 will be applied from the output of tube I08 over line 33 to the pulse forming equipment 24 of Figs. 1 and and to the line selecting equipment 26 of Figs. 1 and 8. However, the energy applied to the line selecting equipment of Fig. 8 will not be passed until such time as line selection has been effected which will be described later.

Line finder 23 having now operated, pulses I09 from line 33 corresponding to the time channel individual to the predetermined line assumed to be calling are applied to an integrating network I III which may or may not be preceded by a pulse stretching circuit similar to a peak voltmeter. These pulses are then amplified in tube III and are applied over transformer II2 to the control grid of the clipper tube H3 and to the control grid of a second tube H4. The integrating network H0 in the input circuit of tube III functions as a low-pass filter which will pass the dial pulses but will not pass the higher frequency communication signals. The clipper II3 serves to shape and clip the incoming dial pulses to form square wave pulses II5 which in turn are differentiated in network H5 and applied to the control grid of dial gate tube I I1. Tube I I1 is biased so as to suppress the negative part of the difierentiated pulse (corresponding to the leading edge of the square dial pulse I I5) and to pass only the positive part of the differentiated pulse, corresponding to the trailing edge of such square wave pulse II5. Normally tube II? is nearly cut-off by the voltage drop in its screen grid resistor II8 which is common with the plate of a normally conducting tube [I9 of a flip-flop circuit which operates in conjunction with tube II4. Time constants of this circuit are so adjusted that the leading edge of the first dial pulse serves to cause tube 4 to operate, cutting off tube II9. Lowpass filter I in the grid circuit of tube H9 causes this condition to be maintained until shortly after the last pulse has passed, when the flipflop circuit will return to normal, again rendering the dial gate tube II'I insensitive. By provision of this special blocking circuit, transient effects before and after dialing will not affect the register. The output pulses from dial gate tube II'I are applied over line 35 to the dial pulse register circuits of Fig. 1, this pulse passing through resistors I2I and I22 to grids of the first register stage.

The dial pulse register circuits consist of a series of tubes of which I23, I24, I25 and I26 are shown in detail connected as conventional trigger circuits for operation as a binary counter. Blocks I21, I28 and I29 constitute further register trigger circuits not shown in detail, there being a sufficient number of these register circuits to count any dialing number in the e::-- change. With the system shown for twenty lines the five shown are suflicient. Initially, the tubes on the right hand side such as I24 and. I26 are conducting serving to bias tubes I23 and I 25 to cut-off. Furthermore, voltages developed in the register circuits are applied as will be described later in more detail over lines I30-I39 to bias the various delay gate tubes to cut-01f and the zero gate tubes to conduction in the line selecting circuit of Fig. 8.

The negative pulses incoming over line are applied to the first register circuit including tubes I23 and I24. When the register circuit is in its normal condition, that is with tube I24 conducting and tube I23 biased to cut-oil, volt age is applied to line I30 maintaining the associated zero device of Fig. 8 in operation and over line I 3I blocking a delay gate to be described in more detail later. The first incoming pulse on line 35 passes through resistance I2I to the grid of tube I24 thus causing this tube to cut-01f rendering, however, tube I23 operative and applying control voltages to lines I30 and I3I which serve to block the first zero gate and open the first delay gate. The output from tube I24 is applied over a line I40 to the second register circuit comprising tubes I25 and I26 serving to transfer conduction from tube I26 to I25 and from I25 to I26 alternately each time the trigger circuit I23, I24 restores to normal condition (i. e. each time tube I24 becomes conductive). It will thus be clear that the second register shifts its condition for every second pulse applied to the first register while the first register changes its condition for every incoming pulse. The third register I21 is similarly controlled over line I 4| so that the register circuit I21 changes its condition each time the second register circuit restores to normal (i. e. each time tube I28 becomes conductive) making register I21 shift its condition once for every two operations of the second register circuit. The fourth register I28 is similarly caused to shift its condition each time the third register I21 restores to normal and the fifth register I28 is similarly controlled from the output of the fourth register I28.

Turning now more specifically to Fig. 8, the operation of these various registers for controlling the delay will be more fully explained. In order to understand the operation of this system it first should be understood that the dials such as I6, Fig. 4, for each line are numbered with digits from 1 to 20 representing the twenty lines. Each dial for any particular line is set so that when a called line is dialed, a number of pulses corresponding to the difierence between the calling line and the called line will be transmitted to the exchange. It thus becomes necessary to produce time displacements in the communication energ corresponding to the difference in timing between the scanning of the two lines in the cathode ray scanning circuit 39. The different signalling pulses operate through the pulse register circuit of Fig. 7 as described above, to select the desired time displacement in accordance with the line which is being called. To this end, each of the register circuits is provided with a zero gate I42, I43, I44, I and I46 associated with thefirst, second, third, fourth andfifth register circuits respectively. Likewise, associated with each of these respective registers are different delay gates I40 microseconds: for the twenty line system), I49 microseconds), I50 microseconds), I5I (40' microseconds) and I52 (80 microseconds). Each ofthese delay gates includes a delay line. In the output of each of these delay lines are delay gate tubes I53 and I54 beingnillustrated in the case of gates I4-8 and I49. It is understood that similar delay lines and gate tubes are provided for the other delay gate circuits. In the normal condition, before any pulse arrives, the system is biased so that the zero gates I42 to I46are all operative so that no delay will be provided in any, ofthe pulses I09 incoming over line 33 from-the line finder circuit of Fig. 6-. Thesepulses I09:therefore will be applied directly from line 33 through the zero gate circuits M2 to I46 inclusive; and fromthere'over"1ine;I55 to the output gate tube I56; Assuming for the moment. that tube I55 is not disabled, its plate delivers corresponding pulses I51 over line 36 tothecontrol electrode of' tube- 39, Fig. 4, and thence back onto the calling line. The first time the first register operates, the control potential is transferred from line I to lineI3I rendering tube I53;con'+ ductive andbiasing'tube. I42 toxcut-oif; Thus, if one pulse only isdialed, a delay of.five microseconds is produced so that the energy'incoming over line 33 will pass through the first delay; gate I48 and the remaining zero gates I43 to I46 inclusive; The second pulse transfers the control potentialfrom line I3I back to I30 causing zero gate I42 again to become operative and blocking tube I53 in delay gate I48. At the same time thesecond register operates. transferrin'g the potential from line I32 to line. I83 blocking the second zero gate I4-3-and opening gate tube I54 in the second delay gate. I49 introducing a ten microsecond delay betweenline '33 and line I55. Thus, the second pulse will pro* duce zero delay. in I42, ten microsecond delay in I49 and .zero delays in I44 to I46. The third incomingpulse willnot affect the second register circuit but will again operate the first register circuit introducing the five microsecond delay gate I48 as well as the'ten microsecond delay gate I49 producing a fifteen microsecond delay inthe incoming energy. The fourth pulse then will return both the first and second register to normal but will operate the thirdregister I2:I producing a twenty microsecond delay at delay gate I50. The fifth pulse'will again insert the five microsecond. delay gate. I48 sothat there will be five and twenty microsecond delays producing a total of twenty five microseconds. The next pulse will switch out the five microsecond delay line and switch in the tenmicrosecond delay line producing a total delay of thirty microseconds. The next pulse will switch in the five microsecond-delay'line while leaving the ten and-twenty microsecond :delayinefiective thus producing thirty five microsecond delay. The next successive pulse willthen render delay lines I48, I49: and I50 ineffective but willb'ring into circuit the fourth delay gate I'5'I with its forty microsecond delay. The othenpulseswill then bring in, in similarsequence, the five; ten and twenty microsecond delay gates I48. I49 and Iioi introducing in sequence five microsecond delays until delay gate I52 is operated whereupon thesprocesswill again be: repeated in five microsecond steps.- Thus,- with the fiVeLdeIay gates it 10 is possible to produce any desired delay condition in the twenty lines. It will be clear that if a different number oflines are provided, additional stages-for the binary counting system and additional zerogates-and delaygates similar to those outlined herein maybe provided to secure the proper delay in interconnection for any number of lines.

After the desired'number has been dialed, the signalling energy fromthe calling subscriber will be transmitted as described over the, common equipment circuit and line 33 in the link circuit to the grid of tube I55. Theoutput pulse I51 from tube its then transferred over line 36 to the control electrode oftube 39 as illustrated. The voice modulations of pulses I51 incoming .over line 38 will then produce variations in the electron stream of tube 39- each time the beam is aligned: withtheocalled line electrode and th s variation in energy will be passed over the line to the corresponding:low-pass filter I9 of the called subscriber to the receiver circuit I8, For the purpose of calling, a tone frequency may be transmitted-to operate any suitable tone control apparatus atthe called subscribers line or the cut ut of receiver is may. be such that attention is directed to the phone directly. by whistle or other call transmitted by thecalling subscriber.

In the foregoingit-has been assumed that tube was conducting, for the purpose of simplicity of explanation. Actually this tube is normally biased to cut-off in order that the dialingpulses incoming overlink'circuit 23 do not affect other lines during the dialing. This cut-off bias of output gate tube I56 is controlled by. the gate control circuit comprising-tubes I53 and I59. Tube. I58 is-normall-y conduetingmaintaining the grid of tube 555 biased'to cut-off. These tubes I58, I59 in turn are controlled by tube II9 as follows: As explained above tube 'I I9 of Fig. 5becomes cut-off at the beginning of a series of dial pulses. At such time it sends out an inefiective positive pulse'through condenser Ifiilto the grid tube I58. As soon as the dialing operation is complete, however, tube H9 returns. to conducting condition sending .out-amegativepulse; This negative pulse-cuts offitube I58; which inturn renders tube-l 5-9; andalscgatewtube- I 55, conductive. This ner-m-jitsthe message energy to be transferred over line i351 to the calledrsubscribersline;

In'order to: protect the called line from being seized by the linevfindersiof other links when the called. subseribers' receiver is removed from the hook, asportion of the delayedpulse 1'51 istapped from linesfi fixovert liner 3:! through isolating resistors IGI in Fig. 4317i) a busy-pulse shaper' l'tz' from whence?=it is conducted to thegrid'of busy gate tub'e IfiSj Tlii's'linritsithe maximum possible value or lth'e' positive line firrcler pulse: se n-0m tube which willbe applied, after theflcalledsubscribe'r raises 'liisreceivento a value which is --insuflicient tooperate the-:line finder gate tube of a, sea-rch'.

ing linerfindera- When-the call is -cornpletediand the calling sub-' seribert hangs up the register circuits of Fig. 7 and the output gate control i5'8 and I59 of Fig. 5 mustbe'restored to normal; This'is done-with tubes I'ESQ 465 and =IE5' of Fig; 7. Wilt-2n the line 2'3 locks in, tube I05, Fig. 6" is drivenato cuton" lowering the potential'on-the grid-of tube #84 over line: 31. This causes the flip-fiop= circuit comprising-tubes I64: and 1 5 65' to operate trans ferring the conductionzto tube I55 A negative pulse is thus: sent over line -I 8 and condenser its to tube its which-is biased tO' cut oH -an'd;

therefore, has no effect. Nowwhen the line finder releases due to the calling subscriber hanging up, tube I95, Fig. 6, again conducts raising the bias on tube I64 over line 3| causing the flip-flop circuit I64, I65 to return to normal. The return of this circuit to normal sends a positive pulse t tube E66 lowering the potential on common resistance I69, thus restoring all of the register circuits and output gate control tube I58, I59 to normal. In order to avoid excessive interaction between various register circuits and output gate tubes, resistor 569 should be sufiiciently low. Then to insure resetting, tube I64 should carry suffciently high currents. This tube may comprise several tubes in parallel.

1 In order to explain the operation of the system, a call will be traced through the circuit from line I to line 5. When the calling subscriber on line I removes the receiver from the hook in his sub-set (not shown), negative potential is applied to the dynode electrode 49. When the beam of tube 39 next traverses contact 49, secondary emission from this contact will produce a pulse in the common anode 69. This pulse then traverses through inverter circuit 89, clipper amplifier 84, cathode follower 85, resistor 81 and line 2'! to the line finder gate tube 88. Line finder gate tube 88 then produces output pulses I which serve to lock oscillator 90 into place with the calling line, Thereafter, the pulses 96 derived from this oscillator (and therefore also the reshaped pulses 98) are maintained in coincidence with input pulses 89. Because of this coincidence, only that set of pulses 89 corresponding to the time channel .of the calling line now under consideration are passed as pulses I00 by the gate tube 88. All other pulses 89 corresponding to time channels of other calling or called lines are suppressed, thus selecting exclusively the pulses of the line under consideration. These selected pulses I00 then serve to operate gate control tube IE3! rendering input gate I58 next conductive, at the correct instants. The output pulses i09 from this tube I08 also represent only the desired ones of all the pulses received from anode 69.

The calling subscriber now dials the number 5 which in this instance produces four successive reductions of the bias on dynode 49. The result is that the particular set of pulses arriving over line H as a result of the scanning of this dynode suffer four successive reduction in amplitude. These pulses are applied over line H, plate circuit of inverter SI, clipper tube 82, cathode follower 83, line 28 to the control grid of input gate I08. Because of the action of clipper tube 82, the four reductions in amplitude of the set of pulses now appear as four complete breaks in this set of pulses. These incoming pulses with their four dialing breaks then are repeated through tube I08 to line 33 as pulses I09. The pulses I09 are transferred over integrating network IIO where the dialing breaks are changed to dialing signals. These dialing signals pass through amplifier III, transformer II2, clipper II3 (where they become square waves I I5). These pass through differentiating network II6, dial gate tube II! and line 35 to the register circuit. Simultaneously, the dialing signals pass through the further integrating circuit I20 to trigger the delay gate mechanism comprising tubes H4 and II9 into abnormal condition (i. e. with II4 operative and II9 cut-oil) and this mechanism increases the positive screen bias of dial gate tube II? so that it will readily pass the pulses I I 5 derived from these dialing signals. The successive pulses II5 then control the first three registers so as to bring the third one to abnormal condition but to restore, the first two back to normal. This inserts delay, gate I50 into circuit producing a twenty microsecond delay equivalent to the time difierence in a cycle of the beam sweep of distributor tube 39 between terminal 49 and output terminal 53 associated with line 5. Simultaneously, the increase in plate potential of tube II8 applies a positive pulse through condenser I60 to gate control I58 and I59; but this has no effect, leaving tube I58 conducting, thus maintaining output gate tube I56 blocked during the dialing interval. As soon as the dialing is completed, the positive potential is removed from the grid of tube H4 restoring delay gate mechanisms II4, II9 to its normal condition with tube I I9 conducting. This reduces the screen bias of tube I I1 preventing further signals from reaching the registers of Fig. '7. Simultaneously the decrease of plate potential of tube I I9 sends a negative pulse through condenser I60 to gate control I58, I58, triggering this to its abnormal condition with tube 58 conducting. This unblocks output' gate 58. The voice signal pulses I09 arriving over line 33 are applied to the output gate tube I56. This tube then delivers output pulses I5! over line 36 to control grid 35 of tube 39 causing the beam to be modulated in amplitude in accordance with the signals incoming over line I each time the beam is in contact with the electrod 53 corresponding to line 5. These pulses varying in amplitude in accordance with the voice signals are then transferred over the corresponding low-pass filter 79 to the receiver I8 of the called subscriber.

When the calling subscriber completes the call and hangs up his receiver, the calling loop circuit is opened and the negative potential removed from electrode 49. When the beam then sweeps past 49 no output pulses will be applied over line II and connections to the line finder circuit will be broken. At the same time, the connection to the line finder circuit is broken, the output from the delay gain tube I 65 terminates, and the control of lock-in oscillator terminates so that the line finder is again free to pick up any new incoming call. At the same time, the potential from the tube I05 is applied over line 3| to the release tube circuit I64, I65. Release Lubes I64 and I65 restore to normalwith I64 conducting. This produces a positive pulse which is transmitted through condenser I68 to tube I66. This applies a restoring potential to the common resistor I69 restoring all the register circuits to normal so that only the zero delay ates 62 to I59 are again operative. Similarly, gate control 158, I59 is restored to normal with tube I58 conducting. Thus, the whole link circuit is ".estored to normal.

In order that the pulses from any one incoming line may be effectively reduced in amplitude so as to prevent other line finders from thereafter seizing the same calling line I, the delayed gain tube I and associated circuit are provided. It will be clear from the above description that when two or more subscribers are using the exchange at the same time there will be a plurality of difierently timed pulses in the line circuits of the common equipment of Fig. 4. These pulses from the output of cathode follower 83 are applied to all of the link circuits in parallel. When one link circuit, however, has taken hold it is necessary that the pulses of this selected circuit be made inefiective to seize other links. A better understanding of the operation of the system 1 3 to- :prevent this operation may' be -=had by'reference to'Figsseand' 6" and the curves illustrated in Fig. I0.

Thetp'ulses from' the"anode'69 of *tube 39 are -a'ppli'ed to the grid 'of tube- 8 [which has separate :plate and cathode outputs. *The pulses-from the plate' output "of'tube 8 I varying in amplitude in 1 accordance with *an 'incoming signal" ar shown in curve WA. Thesepulsesare-clippedin clipper 82at the lever I18 so that only the modulated or "varying amplitude portions ill of the-:pulses a-re passed out'through the; plate circuit ofthistube to cathode rollower'83. --Preferably, the energyis "only about 25% modulated so that the" modulation variations will constitute the-minor portion of-the pulsing energy. These'puls'es are used for transmitting speech and are not 'ofinterest in connectionwith the feature now being considered.

The pulses from the 'ca-thodeoutput oftube 8! "are'the ones of; primary'interest. These pulses are clipped in tube 'iid and-passed through cathode follower--85 so as to produce a series of: equal amplitude -puISesBS-as shown in curve iiiB. These pulses 86 are applied-through resistors it? *aspulsesfidto thegrids "of all line finder gate 7 tubes 8%;in'Fig: 6. Lock-in; oscillator 90. produces an-putput'wave H2, curve lliCiwhosezperiod-us slightly longer than the time'intervalbetween tivor pulses 89. Wave H2 is clippedat clipping "levels lltand H4 then-differentiated'andagain clippedtm produce pulses whose leading edges substantially coincide with the instant 'ofrise of Wave l'iz between the clipping levels. These pulseywhich are. preferably substantially wider than the incoming pulses -89, pass through cathode follower' 91 and the resulting pulses-QS areapplied to the gate tube 88. *Since the f-re- --"quencies areslightly different, the phase or time position of pulses" 89 will-continually shift-with respeot'to pulses 98 until. pulse'89 coincides with "pulse fi-i as' shown in curve' NlD. "Whenthisom the line finder gate 88; Fig.='6,-is operated so that the pulses 1 may? pass through peaked amplifier-1 32 the 'osci'llatoreil'locking it into step' with"thes pulses. The phase correction-of peaked-amplifier "W2- is "-soadjusted that sine wave-112 will rise through" zero-slightly- 'b'e'fore 'the tirne of- 'arrival ofrpulse '89. The-"puIses -SS will then be produced in fixed time relationship --'with'- pulses-89 as shown infirstwaveform of curve 6 13. Qnce' these pulses are synchronized, the' delay gain tube -"Hi cutspff increasing the screen bias of tube-9 5 so-that theseleoting pulses ila-increase from their-normal search=-ampliitude to a 'much higher holding amplitude" as showndnthe-:secondwave-form incurve 56E, thus reducing the efiective heightof pulses 89.

-Thus, pulses89 applied'to the-grids'of line finder gate tubes (corresponding to tube 88) in all other linefinders will be very small as shown 1 inthe third Waveformof curveiilE. Then'even if coincidence-between'these pulses 89-andthe normal tying upan additional link. To :avoid this, the

busy shaper I62;'and" busy gate 163 are =provided which function as follows:

* After--thecompletion of dialing theoutput gate,

EM "tube Hi6 --comme'nces to pass the-speech gpulses I51 oVerline-SE- to control grid -35 0f distributor tube 39 aspreviously described. Part-0f the energy of these pulses I51 is branched fromline '36 in'Fig.8''and passes over-line 3l -and isolating resistor it! to the busy gate shaper' l62,=which amplifies, clips" and-reshapes these-pulses into "strong, sharp constant amplitudepulses. (For this'purpose the clipping level of speechcl-ipper tube- 82 should be set so that the speechmodulation never reduces pulses IT l-below-a small fixed minimum value). The reshaped pulses from It? areapplied to the grid ofbusygate tube 53 to 1 make this momentarily highly conductive. This gatetube "163 then imposes-a fixed upper-limit upon the amplitude of the positive pulses 8Q, so that these cannot attainan amplitude'sufiicient tocauseseizureof the called-lineby anotherline finder. Preferably, however, this upper limit is high enough to hold a line finder-which: has already locked 'i-tself to the vcalled line .(in order that the act of selecting-a line alreadyengaged I as calling line inv apreviousconnection shall'not break downsuch previous connection).

Turning to Fig. 11, I have illustratedlasdelay line in the system where the longer delayse. are required. -Forthe "shorter intervals -shown.-.in delaygates 448,- i49- and- I of-.five, ten-sand twenty microseconds, artificial delay lines- 0f known-form may readily-be used. I-Iowever, for

I the ionger-- delays; acoustic delay means-maylbe preferable. The-line may, for-example -scomprise a container H5 filled with-mercurywilt, having alength where V is' the velocity'ot soundin. the liquid'and D is thew'desired delay time. Atthe inpnt'ienrii provideda "crystaL for: example a quartz :crystal ill,- in a" suitable mounting ring -!:'!,3, with::an electrode 1 l9-coupled-with line :itit for the-=in put signal.

While Ihave illustrated my invention-by way of example in: connection with a particular systemv and-in the form of a single embodiment, it should be distinctly understod fthatzmany Y modifications and applications 0f my invention will occur to those skilled intha art, The-par ticular' embodiment is givenrnerely Ias'. an:.-fexample and is not to'be considered" asa :limitation on myinvention as set forth inhtheobjects thereof and inthe accompanying claims.

I'claim:

. In combination; means for cyclically'producing pulsesgmea'ns for signal modulating-.aspulse -"seri s consistingofa-pulsesduring each ,eycle for given number of cycles, means --for selecting the-signal modulated-pulse series; .a'ga-te circuit means for saidpulses, gate circuitcontrol means responsive tothe first ofthe selected pulses-of the series ioropening said gate circuit. to pass-the selected -pulses;' and--:meansfor maintainingsaid gate-:- circuit open: during J a time?- interval: corresponding to the time of saidigi-ven finumber 0f cycles-o1"- the selectedanodulated pulse-series-only.

-2. -In eornbinatiom means forxcyclically protlucing pulses, means-for =signal=- modulating-ermine series consisting of apulse during: each. cycle s-for a given number of -cycles -rceans 'forrselecting the modulated pulse series; :means fomi reventing ---transients prior to and: succeeding-the eelected modul atedpulse series trom-x passing comprising normally bloclzedv gateirc'uit' means -fon said 7 5 pulsessgate circuit control: means responsivevmo the first modulated pulse of the selected pulse series for unblocking said gate circuit and means maintaining said unblocking condition during a time interval equal to the time of said given num ber of cycles of the selected modulated pulse series only.

3. In combination, a plurality of stations, means for cyclically producing pulses, one for each station, means at each station for signal modulating its pulse, means for selecting the signal modulated pulse series consisting of a pulse during each cycle, means for shaping the modulated pulses into pulses of predetermined polarity and form, a gate tube having input and output circuits, means for normally maintaining said gate tube blocked, means for applying shaped pulses to the blocking means to unblock said gate tube, means for applying shaped pulses to said input circuit whereby each pulse will be operative to produce a pulse in the output circuit during the unblocked interval of said gate tube, and means in the blocking means for maintaining said gate tube continuously unblocked during the period corresponding to the selected modulated pulse series only.

4. The combination according to claim 3, and in which the means for normally blocking the gate tube is a pulse operative trigger circuit, and said means or maintaining the gate tube unblocked is a time constant means for maintaining said trigger circuit operative only during a selected modulated pulse series.

5. In combination, a plurality of stations, means for cyclically producing pulses, one for each station, means at each station for modulating its pulse, means for selecting a pulse series consisting of a pulse during each cycle, means for shaping said modulated pulses into rectangular pulses, a gate tube having a control grid, a screen grid and an output circuit, means for normally maintaining a cut-off bias on the control grid, resistance means coupled to the screen grid for normally producing a resistance drop serving to block the gate tube, a trigger means responsive to the leading edge of a rectangular pulse, a circuit coupling the trigger means to the screen grid to unblock said gate tube, means for differentiating said rectangular pulses to produce positive pulse peaks corresponding to the trailing edges of the rectangular pulses, a circuit for applying the positive pulse peaks to the control grid to produce a pulse in the output circuit of said gate tube during the operation of the trigger means, and timing devices in the trigger means for maintaining it operative only during the occurrence of the selected modulated pulse series.

6. In a telephone exchange system wherein means are provided for cyclically scanning a plurality of lines whereby each line has a predetermined time position in the cycle and register means is provided responsive to incoming calling signals for producing a time displacement in communication signals incoming over a calling line equal to the time difference in said scanning cycle of the calling and called lines, the calling signals having a predetermined frequency characteristic, an arrangement for assuring application of said calling signals, only, to said register means comprising filter means for selecting said calling signals, a gate tube having its output coupled to said register means, said gate tube having a control grid and a screen grid, means for normally biasing said gate tube substantially to cut-ofi, unblocking means coupled to said biasing means normally inoperative to aflect it,

means for applying the selected calling signal pulses to said unblocking means to render it operative to reduce said bias whereby said gate tube becomes conductive upon application of applied signals, means for applying the selected pulses to said gate tube whereby pulses are passed through said gate tube output to said register circuit for each received calling signal pulse, and means operatively associated with said unblocking means for maintaining said unblocking means operative for a period equal substantially to the time period consumed by the train of said calling signals whereby said register circuit will be protected from pulse operation by communication or other transient signals.

'7. In a telephone exchange system wherein means are provided for cyclically scanning a plurality of lines whereby each line has a predetermined time position in the cycle and register means is provided responsive to incoming calling signals for producing a time displacement in communication signals incoming over a calling line equal to the time difierence in said scanning cycle of the calling and called lines, the calling signals having a predetermined frequency characteristic; an arrangement for assuring application of said calling signals, only, to said register means comprising filter means for selecting and shaping said calling pulses, a gate tube having its output circuit coupled to said register means, said gate tube having a control grid and a screen grid, means for normally maintaining a blocking potential on said screen grid, a trigger circuit coupled to said screen grid normally inoperative to affect it, means for applying the shaped calling pulses to said trigger circuit to render it operative to reduce the blocking potential whereby said gate tube becomes conductive upon application of applied signals, means for applying said pulses to said control grid whereby pulses are passed through said output circuit to said register circuit for each received calling signal pulse, and means in said trigger circuit for maintaining said trigger circuit operative for a period equal substantially to the time period consumed by the train of said calling signal pulses whereby said register circuit will be protected from pulse operation by communication or other transient signals.

8. In a telephone exchange system wherein means are provided for cyclically scanning a plurality of lines whereby each line has a predetermined time position in the cycle and register means is provided responsive to incoming calling signals for producing a time displacement in communication signals incoming over a calling line equal to the time difference in said scanning cycle of the calling and called lines, the calling signals having a predetermined frequency characteristic, an arrangement for assuring application of said calling signals only to said register means comprising filter means for selecting and shaping said dial pulses into pulses of predetermined shape, a gate tube having its output coupled to said register means, said gate tube having a control grid and a screen grid, a resistor coupled to said screen grid for normally maintaining a blocking potential on said screen grid, a trigger circuit having a normally non-conductive tube coupled to said resistor, means for applying the shaped calling pulses to said trigger circuit to render said normally non-conductive tube conductive to short circuit said resistor whereby said gate tube becomes conductive upon application of applied signals, means for apply- 18 ing said pulsesto said control grid whereby pulses REFERENCES CITED are passed through 3am gate circuit to lg, The following references are of record in the register circuit for each received calling signal i;

th' pulse, and means in said trigger circuit for main me of is patent UNITED STATES PATENTS taining said trigger circuit operative for a period 5 equal substantially to the time period consume Number Name Date by the train of the calling signal pulses whereby. 2,172,354 Blumlien Sept. 12, 1939 said register circuit will be protected from opera?! 2,387,018 Hartley Oct. 16, 1945 tion by communication or other transient signalslj 2,418,116 Grieg Apr. 1, 1947 DAVID H. RANSOM. 10 

